Gas turbines and steam turbines are regularly inspected to ascertain the state of various parts and surfaces that are liable to deterioration. Most inspections require the gas turbine or steam turbine to be shut down first. An example of this is in the turbine of gas turbines, where a large number of parts such as blades, vanes and seals are subject to extreme conditions such as high temperatures, corrosive atmospheres and high loads. Such parts tend to need regular inspection to check for deterioration or damage but are deep inside a fully assembled gas turbine, and as a result using a boroscope (borescope) may be the most practical way of inspecting these parts.
Although boroscopes are useful for inspection in various places in gas turbines and steam turbines, boroscopes are normally limited to use in low temperatures. Gas turbines and steam turbines, however, normally operate at temperatures of many hundreds of degrees Celsius, and after shut down larger gas turbines and steam turbines can take hours or even days to cool down to a temperature low enough for a horoscope. This tends to result in a long period of waiting between shut down of a gas turbine or steam turbine and inspection using a horoscope. Time spent waiting during an inspection is time during which a gas turbine or steam turbine is offline and not available for use, which is expensive. It has been appreciated, therefore, that it would be advantageous to reduce this waiting time.